How is Radio Useful?
Radio waves transmit music, pictures, conversations and data invisibly through the air. Also, lots of technologies rely on radio waves, such as: AM and FM radio broadcasts, cordless phones, garage door openers, wireless networks, radio-controlled toys, television broadcasts, cell (mobile) phones, GPS receivers, police radio and, thousands more! You may not know this but considering so many things depend on it, radio is a surprisingly simple technology. Actually, you can make simple radio transmitter and receiver with a couple of electrical components!
The Simplest Radio
Did you know you can make radio waves that an AM radio can receive by tapping the terminals of a battery against a coin? Your radio will crackle because of the connection and disconnection of the coin and the battery! You can do this to tap out Morse Code.
A Slightly More Complex Radio
If you want it to get more complex, get a metal file and some wires. Connect a terminal of your battery to the handle of the metal file. Connect the wire to the free terminal and scrape the other end of the wire against the metal file. If you do this in the dark, you will see tiny sparks as the wire goes over the ridges. If you hold the file near the AM radio you will hear a lot of static.
In the early days of radio, transmitters were called spark coils. They created a constant stream of sparks at around 20,000 volts! It made big sparks like the ones in a spark plug. They could travel longer distances as well, but now that is illegal because it takes over other radio stations. It worked fine before it was banned though because not many people used radio waves back then.
How Do Radio Transmitters Work?
To create an even more advanced transmitter, you need to make a constantly changing wave that will always change the EM (Electromagnetic) field.
To change the magnetic field constantly, you need to make a sine wave.
To store information in a sine wave, the wave needs to be modulated (changed). There are three types of modulation – pulse, amplitude and frequency modulation.
Pulse Modulation – The Easy One
Pulse Modulation is basically turning a sine wave on and off!
Amplitude Modulation
Amplitude Modulation is adding two waves together to make a new one, like this:
When the wave is received it is separated into the original two waves, making it identifiable.
Frequency Modulation
Frequency Modulation is making the frequency of the sine wave change. FM radio is clearer than AM radio. Here is a diagram of an FM radio wave:
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